1. Field of the Invention
The invention relates to the field of sensing amplifiers used in conjunction with floating gate memory devices.
2. Prior Art
In MOS read-only memories employing floating gate memory devices, it is common to selectively couple a plurality of these devices to a common sensing amplifier through a column line in the memory array. Typically, the column line is charged; the line is discharged when coupled to a conductive memory device or remains charged if the device is nonconductive. The charge or potential on the line is sensed to determine the binary state (conductive or nonconductive) of the memory device. One such sensing amplifier is disclosed in U.S. Pat. No. 4,094,012, FIG. 3.
The column line when coupled to a conductive device is often allowed to substantially discharge. Before another read cycle, this line must again be recharged. This recharging period reduces the access time in these memories since there is generally considerable parasitic capacitance associated with these lines. This problem is obviously aggravated in larger memories because the column lines have more capacitance.
With the present invention, the potential on the column line is held to a relatively small voltage swing (approximately 0.1 volts), thus considerably less time is required to recharge the column line. A unique biasing circuit and the generation of a reference potential using a "dummy" memory device allows accurate detection despite this small voltage swing.